Photosensitive device



Oct. 13, 1936. T. H. LONG $057,495

PHOTOSENSITIVE DEVIC E Filed Oct. 19, 1932 4 Sheets-Sheet 1 ltcg.z.WITNESSES INVENTOR 7%0/7245 any.

' ATTORNEY Oct. 13, 1936. T. H. LONG PHOTOSENSITIVE DEVICE 4 Sheet-Sheet2 Filed Oct. 19, 1932 INVENTOR fia wdfi i daga WITNESES1 64a ATTORNEYOct. 13,1936.

T. H. LONG PHOTOSENSITIVE DEVICE Filed Oct. 19, 1952 4 Sheets-Sheet 3ig'm INVENTOR 7/?022'45/{1 0 ATTOR EY Oct. 13, 1936.

T. H. LONG PHOTOSENSITIVE DEVICE Filed Oct. 19, 1932 WITNES SES:

4 SheetS-Sheet 4 INVENTOR av U (i 'ATTdRNE Patented Oct. 13, 1936 PATENTOFFICE PHOTOSENSITIVE DEVICE Thomas H. Long, Irwin, Pa., asslgnor toWestinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., acorporation of Iennsylvania Application October 19, 1932, Serial No.638,579

4 Claims.

My invention relates to photo-sensitive devices and has particularrelation to photo-sensitive control systems for machine tools.

A control system for an automatic machine constructed and operated inaccordance with the teachings of the prior art of which I am aware ingeneral includes a support for a worlo-piece' that is to be shaped in apredetermined manner, a support for a tool that is to engage theworkpiece toshape it, and a plurality of motors for moving the tool inthe directions required for shaping the work-piece. The motor iscontrolled by the cooperation of a template that is ordinarily shaped ina manner to correspond to the desired configuration oi the work-pieceand a mechanical pick-up element which is coupled to the controlelements of the motor and which mechanically engages the template insuch manner that the motor controls are properly operated to move thetool support in the manner desired.

A consideration of the systems provided in ac- I cordance with theteachings of the prior art at once discloses a number of disadvantageswhich are inherent in these systems. Among these, the most importantprobably involves the dimculty of suitably coupling the motor controlswith the template through the mechanical pickup. By reason of thedifliculty encountered in this connection, the control system iscomparatively complicated and involves a large number of accuratelymachined levers and switches that are apt to render the operation of thesystem. uncertain and to decrease its accuracy.

Another matter which is ordinarily encountered in the operation ofautomatic machines of the prior art involves the sluggishness ofoperation of the mechanical pick-up and the difficulty of providing asuitable pick-up and so adjusting its coaction with the template thatthe tool accurately and quickly follows the template in responding tothe pick-up.

It is accordingly an object of my invention to .provide a control systemfor an automaticmachine in which the cutting tool shall accuratelyfollow the response of the pick-up to the variations in the contours ofthe template, and by the application of which it shall be possible toshape a work-piece accurately in accordance with desired specifications.

Another object of my invention is to provide a control system for anautomatic machine in which the control elements for the motor and thesystem whereby these elements are coupled to the template shall be ofsimple and tractable structure.

A further object of my invention is to provide for an automatic machinea control system incorporating a pick-up that shall be inertialess, andthat shall be capable of being coupled to the control elements for themotors, whereby the tools are operated, in a simple manner.

A still further object of my invention is to provide for an automaticmachine a control system incorporating a pick-up that shall be sotractable as to be capable of adaptation to the operation of tools ofwidely diverse dimensions.

An incidental object of my invention is to provide an optical system tobe utilized in the control system of an automatic machine, that shall beof such character that by a simple adjustment thereof the system shallbe adapted to be utilized with tools of any desired dimensions.

Another incidental object of my invention is to provide aphoto-sensitive pick-up for the control system of an automatic machineof a type that shall be capable of facile adaptation :for tools ofdifferent characteristics.

Still another incidental object of my invention is to provide a controlsystem for an automatic machine of the type incorporating a pick-upelement and a template cooperating therewith in which the template shallbe capable of utilization as a finish gauge for the work shaped in themachine.

A further incidental object of my invention is to provide an opticalsystem for the photo-sensitive control element of an automatic machine,of a type wherein, bya single operation of a control knob, the apparatusshall be adapted to operate with a cutting tool of any desireddimensions.

An additional incidental object of my invention is to provide for theadjustable photo-sensitive pick-up of an automatic machine a simpleindicating device.

Still another incidental object of my invention is to provide for theadjustable photo-sensitive pick-up of an automatic machine a contrivancewhereby the proper indications .of the adjustment made by the operatorshall be'exhibited without any operation on the part of the operatorbeyond those necessary in the ordinary operation of the machine.

An ancillary object of my invention is to provide a suitable amplifyingsystem for the photosensitive pick-up of the control automatic machine.

A further ancillary object of my invention is to provide an amplifiersystem of the type incorporating electric-discharge devices of the typehaving abrupt characteristics in which the difficulties inherent indrift phenomena that commonly arise in utilizing such electric-dischargedevices shall be repressed.

More concisely stated, it is an object of my invention to provide acontrol system for an automatic machine that shall be of comparativelysimple structure, that shall be capable of accurately and with facilityfollowing templates having a wide variety of configurations and thatshall be capable of adaptations to use with cutting tools of a widevariety of difierent characteristics.

According to my invention, I provide a control system for an automaticmachine in which the pick-up element comprises a source of radiantenergy that cooperates with an optical system to project a radiant imageon the contours of a template and a photo-sensitive device to respond tothe resultant radiant energy emitted by the template. To avoid theinaccuracies which might arise when the radiant beam traverses thecorners and turns of the template, the radiant image projected on thetemplate is of dimensions substantially equal to the dimensions of thecutting edge of the cutting tool. Since the cutting edge of the toolnormally has the.contour of a circular arc, the image is also circularand is of a diameter equal to the diameter of the cutting edge of thetool.

The apparatus for producing the radiant beam utilized in the practice ofmy invention comprises a source of radiant energy, such as an ordinarylamp, an aperture plate which is so disposed as to be illuminated by thesource and a projecting lens which is so positioned relative to theaperture plate as to cast an image of the aperture plate on thetemplate. Since it is desirable that the control system be adapted to beutilized with tools having a wide variety of dimensions, the

element of an .image or the aperture in the aperture plate which isprojected on the template is capable of variations in dimensions. Thedimensions of the image are varied by an adjustment whereby the imaginglens and the aperture and lamp assem-- bly are moved relative to eachother and to 'the template.

To further widen the field of applicability of the pick-up device, anumber of apertiu'e plates having apertures of different dimensions areprovided. Each aperture plate comprises a rec tangular slab near thefour corners of which a plurality of supporting holes are bored. Betweenthese holes iour apertures of different di mensions are bored. The lampis so mounted relative to the support provided for the aperture platethat when the aperture is mounted in any one of the four orientations inwhich it is capable of being mounted, an aperture corresponding to theparticular mounting is illuminated, and is, therefore, imaged on thetemplate.

In the practice of my invention, three aperture plates are generallyprovided. Each aperture plate is equipped with four apertures which areof diameters that are simple multiples of each other. In practice Iprefer that the diameters of the larger apertures of any one plateshould be respectively two, four and eight times the diameter of thesmallest aperture. The apertures of the difierent plates are so relatedto each other that the total range of tool dimensions is subdivided intoa series of overlapping regions, each {region corresponding to the imagedimensions that can be obtained with a single aperture by varying theoptical system over its whole range. Specifically, the ratio of thediameters of {corresponding holes of two plates is as the nth root of ois to 1 where n is the number of plates and o is the ratio of successiveaperture diameters in any one plate. Thus in the present case the ratiois a/Ei.

The contrivance whereby the dimensions of the image projected on thetemplate are varied comprises a hand knob which is coupled to thesupports for the imaging lens and lamp and aperture, in such manner thatby simple rotation thereof these elements are moved relative to eachother. A circular plate having a plurality of dial indications thereonis mounted concentric with the knob and rotates therewith. The dialscales are three in number, each corresponding to the largest apertureof an aperture plate. Given the indication for any particular setting ofthe knob, the dimensions of the corresponding image may therefore becalculated from a knowledge of the particular aperture of an apertureplate that is utilized.

The aperture plates are equipped with grooves which are so disposed thatwhen two of the aperture plates are mounted in position they cover thescales which correspond to them, leaving open to view the scale whichcorresponds to the aperture plate mounted in operative position.

The radiations projected across the contour of the template impinge onthe sensitive element of a photo-sensitive device. A toothed disc isrotated in the path of the beam and as it rotates it produces apredetermined number of interruptions in the beam. The interruptionsthus produced result in pulsations in the output of the photo-sensitivedevice subjected to the beam and render the output of thephoto-sensitive device capable of amplification by an a1npliher of thealternating-current type. The output of the amplifier is impressedbetween the control electrodes and the principal electrodes of aplurality of gas-filled electric-discharge devices of thegrid-controlled type, in such manner 'as to energize the devices inaccordance with the magnitude of the output.

The electric-discharge devices are so connected as to excite the relayswhereby the clutches, for coupling the driving motors to the propergears to motivate the tool support in the desired directions, arerendered operative. The systern involving the clutches does not concernthe present invention, and for this reason, is not described herein.However, it is shown and described in a copending application, SerialNo. 659,120, filed March 1, 1933, to O, G. Ruterniller and myself.

' The apparatus whereby the radiant beam is produced and thephoto-sensitive device are so mounted as to movewith the tool support,while the templet is fixed. When the optical elements are so positionedrelative to the template that the template completely obstructs the beamthe electric discharge devices'are deenergized and the particular clutchin operative relation with the motor produces a motion of the toolsupport such that the tool moves normally towards the work-piece. Afterthe optical elements have been displaced a distance dependent on thecharacter of the template and a predetermined minimum amount of radiantenergy projects The outward motion is produced when the excitation ofthe photo-sensitive device is increased to the predetermined valuegreater than the value for which the traverse motion takes place. Insuch a case -a second set of electric-discharge dew'ces becomeenergized. When this set of electric discharge devices becomes energizeda system oi. relays is energized to operate the necessary clutches tointerrupt the traverse motion and initiate the outward feeding, motion.

A third set of electric-discharge devices is provided for the purpose ofstopping the entire system when an excess of light impinges on thephoto-sensitive device. Such a situation occurs, for example, when thetemplate has by some inadvertence been removed from its proper position,in which case, it is desirable that the tool and the machine should bestopped.

It will be noted that the gas-filled electricdischarge devices utilizedin the practice of my invention are connected in pairs. This arrangementis essential by reason of the fact that gasfilled devices of thegrid-controlled type have what has been designated as a driftcharacteristic. It has been found that after a gas-filledelectric-discharge device has been utilized for some time its-propertieschange in such manner that its potential-response characteristic isvaried, that is to say, a gas-filled electric-discharge device at aparticular time becomes energized for a certain circuiting distributionof potential between its electrodes. After it has been utilized for acomparatively long period of time, its response characteristic is variedand it becomes energized for another limiting distribution of potentialbetween the electrodes which. may be and generally is considerablydifierent from the first distribution.

If a single electric-discharge device were utilized for each actuationof the clutches in the practice of my invention, the driftcharacteristic might occasion considerable difliculty in view of thefact that when the electric-discharge device changes in any manner, itsresponse to the excitation of the photo-sensitive device might change,and for this reason, the system might respond to the excitation of thephotosensitive device in a manner contrary to expectation. Thus theinward motion of the tool might be initiated when the traverse motionshould continue or thetraversemotion might be initiated when the outwardmotion should continue. To eliminate this difficulty, the systemutilized in the practice of" my invention is provided with pairs ofelectric-discharge devices.

One device is utilized only for the purpose of initially responding tothe condition of the electric-discharge device, and is immediatelythereafter deenergized. However, before it is deenergized, it causes thesecond device to become energized and to produce the necessaryexcitation of the controlling relays. The range of variation ofpotential which is impressed by the excitation of the firstelectric-discharge device on the electrodes of the secondelectric-discharge device is of sufllcient magnitude to produce thenecessary changes in the second electric discharge device, regardless ofthe drift characteristic.

The novel features that I consider characteristic of my invention areset forth with particularlty in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of a specificembodiment when read in connection with the accompanying drawings, inwhich:

. Figure l is a view in perspective showing the essential elements'of acontrol system for a machine constructed in accordance with myinvention;-

Figs. 2, 3 and 4 are diagrammatic views showing the relationship betweenthe dimensions of the image projected on the template and the dimensionsof the cutting tool;

Fig. 5 is a view in front elevation showing an optical systemconstructed in accordance with my invention;

Fig. 6 is a view in side elevation of the optical system shown in Fig.5;

Fig. '7 is a view in perspective showing the essential elements of theoptical system shown in Fig. 5;

Fig. 8 is a detail view in paspective showing the essential elements ofthe indicator utilized in the practice of my invention;

Fig. 9 is a view in perspective showing a portion of an aperture plateutilized in the practice of my invention;

Fig. 10 is a view in front elevation showing a photo-sensitive systemconstructed in accordance with my invention;

Fig. 11 is a view in side elevation of the photosensitive assembly shownin Fig. 10;

Fig. 12 is a diagrammatic view showing the circuit of thephoto-sensitive device and its associated amplifying elements that isutilized in the practice of my invention.

The apparatus shown in Fig. 1 comprises a lathe l incorporating theusual elements, to-wit, a support 3 for a cutting tool 5 and a support 1for a work-piece (not shown), to be shaped in a predetermined manner.The cutting-tool support 3 is equipped with the ordinary adjustments andis motivated by a motor (not shown), through. a system of clutches andgears in a manner depending on the disposition .and the desiredstructure of the piece to be shaped. The motor and its coupling do notconcern the present invention and are for this reason not shown. Thecutting-tool support 3 is equipped with a slotted extension 9 in which abracket II is adjustably secured. A container l3 having disposed thereinthe elements of the optical system, which will be described in detailhereinafter, is secured to an upper flange l5 of the bracket ll while acontainer II, in which a photo-sensitive device l9 and certainamplifying elements 2| also to be described in detail hereinafter aredisposed, is secured on. a lower flange 23 of the bracket II. A beam ofradiant energy is projected through an opening in the container l3 ofthe optical system and passes through an opening 25 in the container 23of the photo-sensitive system, thereby energizing the photo-sensitivedevice l9.

The output of the photo-sensitive device it is suitably amplified by asystem of high vacuum and gas-filled electric-discharge devices, and theoutput of the amplifier is fed into the exciting coils 21, 29 and 3| ofa series of electromagnetic relays 33, 35 and 31 to actuate thenecessary clutches and thereby to produce the necessary motion of thetool support 3.

The manner in which the clutches are to be coupled to the motor wherebythe tool support is to be motivated is dependent on the particularmachine utilized and should be apparent to one skilled in the art anddesiring to apply my invention to a particular machine. To discuss themanner in which the machine is operated from the clutches would,therefore, be superfluous in the present state of the art, and wouldrender the specification unnecessarily verbose.

It is to be noted that since the containers i3 and I1 for the opticalsystem and for the photosensitive system are both secured to the toolsupport 3, they are therefore movable therewith and follow the motion ofthe tool 5.

A template 39 of structure corresponding to the shape of the work-piecethat is desired is secured to a clamp 4| suitably mounted in a vise 43which in turn is slidably supported in a track 45 secured to the lathe Iand is thus capable of proper positioning in the lathe. When properlypositioned the template 39 is so oriented that its edge 41 that is socut as to correspond to the desired final configuration of thework-piece, intercepts or partially intercepts the beam of radiationsprojected from the container l3 for the optical system. The movement ofthe tool support 3 and, therefore, of the tool 5, is predetermined bythe extent to which the beam of light is intercepted by the edge 41 ofthe template 39. The beam of light is movable relative to the template39 and it is, therefore, capable of tracing out in space a cylindercorresponding to the edge 41 of the template 39. The interaction betweenthe beam, the photo-sensitive system and the template 39 is such thatsubstantially such a cylinder is traced. At the same time the cuttingedge 49 of the tool 5 which moves with the beam of radiations traces acurve corresponding to the configuration of the guiding edge 41 of thetemplate 39 and when in engagement with the work-piece shapes the latterto correspond to this configuration.

The template 39 is of such structure that projecting portions of itscontrolling edge 41 correspond to the indentations to be milled on thework-piece and the indentations of its controlling edge correspond tothe projections in the final work-piece. This procedure is followed toprovide for the accurate correspondence of the movement of thecutting-tool 5 with the movement of the light beam. For proper operationof the system the light beam should. cut the same configuration in spaceas the cutting-tool 5 cuts out in the work-piece.

answers impinging on the photo-sensitive device I9 is greater than apredetermined value. 0n the other hand, when a predetermined minimumradiant flux is less than the predetermined value projected on thephotosensitive device H, the tool 5 is moved neither in nor out but in adirection transverse to the worlr-piece.

The operation of the system can probably best be explained withreference to the central projection 5| of the template 38 shown inFig. 1. Assume for example that the beam oi light is totally obstructednear the inside terminal '53 of the central projection 5i, and that whenmoving transverse to the work-piece it moves in a direction away fromthe plane of the drawing. The tool 5 will then move in an inwarddirection and the beam of radiant energy will be gradually displacedrelative to the template 38 in such manner that a small amount ofradiant energy is ultimately projected over the edge 41 of the templateonto the photo-sensitive device 19. As soon as the necessary minimumflux impinges on the photo-sensitive device IS, the photosensitivesystem is so actuated that the inward motion is arrested, while thetransverse motion is initiated. As the tool 5 is therefore moved in atransverse direction, the beam of light is again obstructed completely,the necessary relays of the photo-sensitive system are again actuatedand the transverse motion is stopped, while the inward motion is againinitiated. The same process is repeated until the tool 5 attains such aposition that the beam of light is obstructed by the region of thestationary point of the central projection 5| of the template 39.

At this point, the inward motion is again stopped and the transversemotion is again initiated. However, by reason of the fact that the sideof the projection towards which the beam of light is now moved slopes ina direction opposite to the direction in which the other side slopes,the flux impinging on the photo-sensitive device 19 is increased by thetransverse motion of the tool 5 rather than decreased. For this reason,the flux impinging on the photo-sensitive device 19 soon attains a valuefor which the transverse motion is stopped and outward motion isinitiated. By reason of the outward movement of the beam of lightrelative to the template 31, the total flux projected on thephotosensitive device is ncw decreased until the minimum value isattained for which the outward motion is arrested and the transversemotion is again initiated. This process is repeated until the beam oflight is obstructed by the region adjacent the outer stationary point 41of the projection 51. At this point the beam of radiant energy begins toclimb up on the successive projection 59 of the template 33 and the toolbegins to move correspondingly.

It will'be noted that in operation the radiant beam of the pick-upelement moves along the edge of the template 31 in small steps,corresponding to the motion of the tool. That is to say, the path of thepick-up element is made up of a series of short straight lines, eachstraight line at right angles to the successive straight line and thewhole series of straight lines tracing out a curve corresponding to theedge of the template.

The image Bl that is projected on the template 39 by the light beam issubstantially identical in form to the configuration of the cutting edge49 of the cutting tool 5. In general, the cutting edge 49 is of circularform and the image is correspondingly of circular form, the diameter ofthe beam being substantially equal to the diameter of the cutting edge89 of the tool 5. This condition is necessary to eliminate dimcultieswhich might otherwise arise in cutting corners.

In Figs. 2, 3 and 4, the difliculties which arise in cutting a turn or acorner in the work-piece are illustrated diagrammatically. In Fig. 2, aportion of the guiding edge 41 of the template 39 is shown and an image63 of a light source having a diameter smaller than the diameter of thecutting edge 49 of the cutting-tool 5 is shown as impinging on the edge41 in two successive regions. As the light beam moves relative to thetemplate 39, the image moves out along the curve 41.

In Fig. 3 a corresponding portion of the workpiece 65 is shown in itsdesired configuration and two positions which the tool 5 assumesrelative thereto are shown. The positions correspond to the positions ofthe image 83. It will be noted that the image 83 and the tool 5 areshown in Figs. 2 and 3 as having moved from a rectilinear portion of thetemplate and work pin adjacent to a curved portion, to the curvedportion. In the first of these positions the template 39 obstructs thebeam while in the second of these positions, the beam projects over theedge 41 of the template since the direction of motion of the tool is notaltered until sufficient radiant energy is projected over the edge "ofthe template 39 to suitably energize the photo-sensitive device. Thetools project over the desired edge of the work-piece 85 in itsdisplaced position. If, therefore, the image 63 is of smaller diameterthan the cutting edge 49 of the tool 5, the countour which the tool willfollow, will correspond to the envelope of a series of tool positionsrepresented by the tool shown in Fig. 3 and, will not correspondaccurately to the configuration of the template 39. ency occurs if theimage 83 is of larger diameter than the cutting edge 49 of the tool 5.

In Fig. 4, a section of the template 39 is shown as it appears whenintersected by an image, the diameter of which is equal to the diameterof the cutting edge 49 of the tool 5. As will be noted in comparing thisview with Fig. 3, the movement of the tool is controlled by theperiphery of the image and when the periphery of the image projects overthe template 38 by a predetermined amount, the direction of motion ofthe cutting tool is properly adjusted. Thus,

before the cutting tool can be projected to such an extent as tomaterially vary the configuration of the work-piece from that desired,its direction of motion is changed by reason of the fact that suflicientlight is projected over the edge 41 of the template 39 to properlyenergize the photosensitive system. The cutting tool 5, therefore,accurately follows the contour of the template 39 and the finalconfiguration of the work-piece accurately corresponds to the contour ofthe determining edge 41 of the template. I

The cutting tools utilized in the practice of my invention are not ofthe same diameter and as a matter of fact, vary widely in diameter. I

have, therefore, been confronted with the problem of providing anoptical system for so varying the diameter of the cross section of thelight beam that my invention can be practiced with cutting tools ofwidely diverse dimensions. v

The optical system provided in accordance with this feature of myinvention is shown in A corresponding discrep-.

detail in Figs. 5 to 9, inclusive. As. can be seen from these views, itcomprises essentially a light source 81 preferably anjncandescent lamp,with a small filament 69, a condensing lens II, and aperture plate I3 ofsuitable character and a projection lens I4 whereby the image of anilluminated aperture I5 in the aperture plate is projected on thetemplate 39. The condensing lens II and the aperture plate I3 aresecured to a bracket 11 and the source 61 is supported on a projectionI9 of the bracket 11. The bracket 11 is, in turn, equipped with ears 8|that are engaged by the terminals of a bow spring 82 the face of whichengages one rail of a track 83. The bracket II. is thus held in slidableengagement with the track 83. The bracket I1 is moreover maintained onthe track 83 by a plurality of plates 85 which are secured to the track83 and project over the sides thereof to engage the projecting ears 8|of the bracket 11. It is seen that, as the bracket 11 is moved along thetrack 83, the position of the assembly comprising the source 81 thecondensing lens II and aperture I5 is changed.

The projection-lens assembly is mounted on a bracket 81 similar to thebracket 11 on which the lamp assembly is mounted. The bracket 81 is alsomaintained in engagement with the track by a bow spring 89, theterminals of which engage a plurality of cams 9I extending from thebracket and the side of which engages one rail of the track 83. It ismoreover held on the track by a plurality of plates 93 that are securedto the track 85 and engage the ears 9| projecting I laterally from it.

The lamp assembly and the imaging lens assembly are moved relative toeach other and relative to the template 39 by the engagement of theprojecting ends 95 and 91 of a. plurality of rods 99' and I M secured tothe brackets II and 99 and I8I, in engagement with the cams I83 and I85is changed and the position of the supporting brackets TI and 81 for thelamp assembly and for the-lens assembly are correspondingly changed. Itis to be noted that as the positions of the aperture plate I3 and of theprojecting lens I4 are changed relative to the template 39, thedimensions of the image projected on the template are changed and thesystem is thereby adapted to be utilized with cutting tools 5 ofdifferent dimensions.

The cam plate III may be locked in any one of aplurality of positions bythe engagement of a slotted stud member I II which screws into the track83, with a disc sector H9 which is mounted on the shaft ml of the camplate MI. The locking stud III is equipped with a suitable handle I23which renders it capable of being easily manipulated.

The aperture plates 53 are substantially rectangular and each plate isequipped with four holes I25 so milled that the lines drawn throughholes I25 and as will be apparent, the particular aperture 15 that isutilized at any particular time is dependent on the orientation of theaperture plate 13 in the supporting bracket 11.

In the practice of my invention, I have pre Ierred to maintain theapertures I5 of diameters, that are multiplied by two of each other, thesmallest aperture 15 having a diameter that is of the diameter of thelargest aperture on any particular plate 13. It is seen that byutilizing a single plate 13 in its various possible orientations and inaddition by applying the adjustments provided in the system, the systemis adapted to be utilized with a wide variety of cutting tools 5.However, in the practice of my invention, I have found it necessary toutilize three aperture plates rather than a single plate. Two of theseplates are ordinarily supported in a storing position as shall bedescribed hereinafter while one plate is supported in operativeposition.

It is essential that the optical system be provided with a calibratedscale for indicating the diameter of the aperture image corresponding tothe various positions of the adjusting knob H9, and the provision ofsuch a scale for the numerous apertures raised a considerable problem.The scale constructed in accordance with my invention comprises a plateI29 having series of dials I3I, I33 and I35 ruled thereon. The plate I29is mounted concentrically with the knob II3 whereby the cam plate III isrotated.

Each dial, I3I, I39 and I95 is calibrated to read the dimensions of theimage of the largest aperture 15 of a single aperture plate 13. Theimage dimension which corresponds to a particular setting or a dial whenthe aperture plate 13 is so oriented that any other aperture when thesmallest one is being projected on the template 39 may be obtainedsimply by dividing the reading of dial by 2, 4 or 8 depending on theparticular aperture utilized.

The indicating disk I29 may be observed through an opening I31 in thecontainer I3 0! the optical. system and the particular dial I3I, I99 orI35 corresponding to the plate 13 which is in operative position isvisible through the opening while the other dials are covered by thesides of the aperture plates 13 which are not being utilized and whichare, therefore, supported in storing position adjacent to the dial diskI29.

To provide for the exposure to view of the proper dial, the apertureplates 13 are equipped with slots I39. The slots I39 in one plate are sopositioned that the two upper dials I3I and I39 are visible through theplate 13 when the plate is mounted in storing position; the slots I99 inthe second plates 13 are so positioned that the lower two scales I33 andI35 are visible through the plate when it is mounted in storing positionand the slots I39 in the third plate 13 are so positioned that the upperand lower scales I3I and I35 are visible through it while the centralscale is covered when it is mounted in storing position. When two of theplates I3 are superposed upon each other in storing position, only oneof the dials I3I, I33 or I35 remains visible through the superposedplates and this dial corresponds to the particular aperture plate 13that is mounted in operative position. It is seen that to accomplishthis object, the

upper scale I3I must be made to correspond to aomnos scale I39 mustcorrespond to the plate 13 in which the slots I39 are so cut as to leaveexposed to view the upper and lower scales I3I and I35 and the lowerscale I35 corresponds to the plate 13 in which the slots I39 are so cutas to leave exposed to view the upper and central scales I H and H3.

The utilization of the optical system is apparent from the abovedescription. The particular plate 13 to be utilized is mounted in. theposition provided therefor on the bracket 11 while the other plates 13are mounted in storing position. The hand knob H3 is then turned untilthe proper scale indicates the diameter of the cutting edge 49 of thetool that is to be utilized and the system is then. looked in position.In its locked position, the optical system is thus adapted to beutilized with the tool for which it was thus adjusted.

The photo-sensitive unit is shown in detail in Figs. 10 and 11. As shownin these views, the unit comprises in addition to the photo-sensitivedevice I9, a light chopper I4I that is rotated from a motor I 43 ofsuitable character and is so mounted within the casing I1 that its teethI45 interrupt the light which is projected through the opening 25 on thecathode I41 01 the photo-sensitive device I9. The light thus interruptedexcites the photo-sensitive device I9 and the output oi! thephoto-sensitive device is amplified by a plurality of high vacuumamplifiers 2I, I5I, I53 and I55; the first one 2|, of which is mountedcontiguous to the photo-sensitive device I9 to eliminate anydiiiiculties which might otherwise arise from capacity losses inherentin long leads extending from the photo sensitive device to the amplifier2| Suitable partitions I59 are provided in the container I1 to isolatethe photo-sensitive device I9 from the amplifier 2I and from the otherelements of the system.

The complete amplifier that is preferably utilized in the practice of myinvention is shown in detail in Fig. 12 and includes in addition to thehigh vacuum amplifiers 2|, I5I, I59 and I55, the resistors I M, I63 andI85 and the capacitors 191, I99 and HI whereby the amplifiers arecoupled to each other. The last amplifier I55 is coupled to a gas filledelectric discharge device I13 preferably of the grid glow type through acapacitor I15 and a resistor I11 and its out put potential is impressedbetween the control electrode I19 and the cathode I9I of the device I13.When the fiux impinging on the photosensitive clevice I9 attains a valuewhich is determined by the setting of a potentiometer I92 coupled to thecontrol electrode I19 of the gasillled device I19, the device becomesenergized and current is transmitted between the cathode I BI and theanode I93 thereoi'.

However, a capacitor I85 of suitable magnitude to correspond to theoutput of gas-filled device I13 is connected in series with itsprincipal electrodes IBI and I83 andas current is transmitted throughthe device, the capacitor I95 is charged and eventually a potential ofsuch polarity as to oppose the current between the principal electrodesI9I and I93 01' the device I13 is impressed on its plates and the devicebecomes deenergized. Before this condition occurs, a second gas-filledelectric discharge device I91 is energized by reason of. the change inpotential impressed between its cathode I99 and its control electrodeI9I by the current flow through the first electric discharge device I13.

The second gas-filled device I81 is coupled to the first device I13through a capacitor I93 of suitable magnitude and through a resistor I95and these elements are so adjusted that, regardless of variationsintroduced in the characteristics of the second device I81 by aging, theexcitation of the first device I13'produces sufllcient change inpotential to energize the second device.

The principal circuit of the second electric discharge device I91 isconnected through the exciting coil 21 of the relay 33 and when thisdevicebecomes energized the relay 33 becomes excited and, its movablecontactor I91 is disengaged from a plurality of corresponding fixedcontacts I99. and engages another set of fixed contacts 20l By thedisengagement of the movable contactor I91 from the first set of fixedcontacts I99, the clutch (not shown) whertbythe inward or outward feedof the motor was maintained is rendered inoperative and by theengagement of the movable contactor I91 with a second set of fixedcontacts 2!, the traverse feed is initiated.

It is seen that the system involving the gasfilled electric dischairgedevices I13 and 481. is so adjusted that the first device I13 does notcarry current for any appreciable length of time and has therefore,generally a characteristic which may be depended upon to remain unchanged. The second device I91 on the other hand, while it must ofnecessity remain energized for considerable periods of time, is notdependent upon its excitation for small changes in the potentialsimpressed on the control circuit thereof but depends for its excitationsimtively large change which occurs when the first electric dischargedevice I13 passes from a de energized condition to an energizedcondition. The difliculties with aging which I have observed and which Ihave encountered in utilizing gasfilled electric-discharge devices arethus avoided and the frequent replacements or changes in the circuitwhich would otherwise be necessary are obviated.-

The system is supplied with power from a transformer 295 through arectifier 201 and a system of filters 209. It is a well known fact thata gas-filled electric-discharge device when once energized by avariation of the potential applied to its control circuit remains in itsenergized condition regardless of the changes introduced in thepotential of the control circuit until the potential between theprincipal electrodes is' reduced to a value smaller than the value ofthe cathode drop of potential required to maintain the device inenergized condition. Since the system in the present case is operated bydirect current power supply, it is essential that some external means beprovided for maintaining the gas-filled electric-discharge device in acondition continuously responsive to the variation in potential appliedto the control electrodes thereof.

For this purpose, interrupters ii I, H3 and 2I5 are provided. Oneinterrupter 2H is coupled across the capacitor I35 whereby the firstelectric-discharge device 813 is deenergized and it short circuits thecapacitor I 85 at a rate which is large compared to the rate at whichchanges occur in the radiant fiux projected on the photo-sensitivedevice I9 by reason of the cooperation of the light beam andthetemplate;

39. It is seen that the interrupter 2H continues to maintain thecapacitor in discharged condition and the electro-discharge device I13associated with the capacitor I85 is maintained in a condition such thatits control circuit is always responsive to the state of excitation ofthe photo-sensitive device I 9.

The potential applied to the principal circuit of the secondelectric-discharge device I81 is periodically reduced by an interrupter2I3 comprising a rotating disk 2I1 equipped with insulating inserts 2I9.The disk 2I1 is rotated at such a rate that the circuit is broken by theinserts at a frequency that is great compared to the rate at which theflux impinging on the photo-sensitive device I9 is changed by thetemplate 39. This circuit is, therefore, also maintained continuouslyresponsive to the condition of the photo-sensitive device I9.

It is seen that by the action of the interrupter 2II the firstelectric-discharge device I13 will be energized and deenergized continu-.for an instant deenergized by the rotation of the switch 2I3. On'theother hand, if after the switch 2| 3 has broken the principal circuit ofthe second electric-discharge device I81, the first electric dischargedevice I13 does not become ener'gized for a considerable period of time,the second device I81 will also remain deenergized and the relay 33associated therewith will be deenergized.

When the flux of the radiations impinging on the photo-sensitive deviceI9 becomes greater by a predetermined amount than the minimum 'value forwhich the first set of electric-discharge devices I13 and I81 becomeenergized, the electric-discharge devices 22I and 223 of a second setbecome energized. The fiux for which the devices HI and 223 becomeenergized is regulated by the setting of a second potentiometer225.a,ssociated with the first device 22l of this set that is similar tothe corresponding potentiometer I82 which is associated with the firstdevice I13 of the set which has been described hereinabove. Theoperation of the devices 22'I and 223 is similar to the operation of theother set. When the second device 223 of the set becomes energized, therelay 35 is excited and the necessary clutch for producing the inwardmovement of the tool 5 is rendered operative, while the clutch forproducing the traverse motion of the tool 5 is rendered inoperative.

A third set of devices 221 and 229 similiar to the first two sets areprovided for the purpose of stopping the machine when the excitation ofthe photo-sensitive device I9 is greater by a predetermined amount thanthe excitation necessary for energizing the second set ofelectricdis'charge devices 22I and 223. The third set of devices isprovided for the purpose of stopping the machine in contingencies orwhen the tool support is in such a position that the beam of light hasjust passed over a terminal of the determining edge 41 of the template39. The exciting coil 3! of the relay 31 whereby all the circuits areopened is connected in the principal circuit of the secondelectric-discharge device 229 of this set. i

The explanation of the operation of the relay system shown in Fig. 12,has been given in detail hereinabove. When the template 39 and opticalsystem are so disposed relative to each other that the photo-sensitivedevice I!) is substantially deenergized, the controlling relays are inthe positions shown in the view and the tool 5 is being fed in an inwarddirection. When the flux impinging on the photo-sensitive device Hi isof such magnitude that the first set of electric-discharge devices I13and I81 are energized, the corresponding relay 33 is energized and theinward feeding of the tool 5 is arrested while the traverse feed isinitiated. On the other hand, when the light flux impinging on thephoto-sensitive device i9 is such that both the first and second set ofgas-filled electric-discharge devices are energized, the correspondingrelays 33 and 35 are in excited-condition and the traverse feed isinterrupted while the outfeed is initiated. correspondingly, when theflux impinging on the photo-sensitive device I9 is such that the thirdset of electric-discharge devices 221 and 229 are energized, themovement of the tool 5 is entirely interrupted.

Although I have shown and described certain specific embodiments of myinvention, I am fully aware that many modifications thereof arepossible. My invention therefore, is not to be restricted, exceptinsofar as is necessitated by the prior art and by the spirit of theappended claims.

I claim as my invention:

1. Translating apparatus comprising an electrio-discharge device havinga plurality of electrodes said'device being of the type that has anenergized condition and a deenergized condition and is capable only ofabrupt transition from one condition to the other as the potentials1mpressed between its electrodes'is varied, a network through which saiddischarge device is to pass current for an appreciable length of timewhereby said device exhibits a drifting characteristic that is evidencedby a variation in the distribution of potential between its electrodesfor which it changes its condition at different times, means forimpressing potentials between the electrodes of said electric-dischargedevice that are of such magnitude as to maintain said device in one ofsaid conditions regardless of said drifting characteristic, means forchanging the condition of said device, said means including: a secondelectric-discharge device having a plurality of electrodes, said devicebeing of the type that. is capable of abrupt transition from onecondition to the other, means for impressing potentials between theelectrodes of said last-named electric-discharge device to maintain saiddevice deenergized thereby to maintain said first-named device in one ofits conditions and means for so coupling said lastnamedelectric-discharge device to said firstnamed electric-discharge devicethat when said last-named device is energized the change in potentialproduced between the electrodes of said first-named device is sufficientto at all times immediately change the condition of said firstnameddevice regardless of the drifting characteristic oi said first-nameddevice, means for varying the potentials impressed between theelectrodes of said last-named electric discharge device to energize saidlast-named device thereby to vary the condition of said first-nameddevice and means for deenergizing said last-named device immediatelyafter it has produced a change in the condition of said first-nameddevice whereby said last--named device does not exhibit a driftingcharacteristic.

2. Translating apparatus comprising an electric-discharge device havinga control electrode and a plurality of principal electrodes said de--vice being of the type that has an energized condition and adeenergized condition and is capable only of abrupt transition from onecondition to the other as the potentials impressed between itselectrodes are varied and that exhibits a drifting characteristic thatis evidenced by a variation in the distribution of potential between.its electrodes for which it changes its condition at different timeswhen operated in an energized condition for an appreciable length oftime, means for impressing potentials between the electrodes of saidelectric-discharge device that are of such magnitude as to maintain saiddevice in one of said conditions regardless of said driftingcharacteristic, means for changing the condition of said device, saidmeans including: a second electric-discharge device having a pluralityof electrodes, said device being of the type that is capable of abrupttransition from one condition to the other, means for impressingpotentials between the electrodes of said lastnamed electric-dischargedevice to maintain said device deenergized thereby to maintain saidfirstnamed'device in one of its conditions and means for so couplingsaid last-named electric discharge device to said first-named electricdischarge device that when said last-named device is energized thechange in potential produced between the electrodes of said first-nameddevice is sufiicient to change the condition of said firstmamed deviceregardless of said drifting characteristic; means for varying thepotentials impressed between the electrodes of said last-named electricdischarge device to energize said last-named devide thereby to at alltimes immediately vary the condition of said first-na1ned device andmeans for deenergizing said last-named device immediately after it hasproduced a change in the con dition of said first-named device wherebysaid last-named device does not exhibit a drifting characteristic.

3. Apparatus according to claim 2 characterized by the fact that thedeenergizing means for the last-named discharge device includes acapacitor to be discharged by the current transmitted by the last-nameddischarge device.

4. Apparatus according to claim 2 characterized by the fact that thedeenergizing means for the last-named discharge device includes acapacitor to be discharged by the current transmitted by the last-nameddischarge device, and means for periodically discharging said-capacitorto render said last-named discharge device periodically responsive tothe means whereby it is energized.

THOMAS H. LONG.

